Application of Calculus in Non Continuous Physical Systems

In the mathematics of Calculus, a basic requirement is that the system or function should be continuous. Until the discovery that matter is discontinuous, applying Calculus in Physics was reasonable. But why is it still applied almost everywhere in physics ? Won't such applications produce erroneous results ?

Does it mean that some form of matter is continuous ? Matter, as we all know, is made up of atoms. So it is discrete and discontinuous. So I believe that application of Calculus is inappropriate in areas like Gravitation, Electromagnetism and Nuclear Physics.

Well, I can't argue with your beliefs, but I reject them. Application of the calculus to the problems you mention has been quite successful. You assume that atoms behave independently regardless of circumstances. Your assumption that the calculus can deal only with mathematically continuous systems is also faulty. You also have not provided any examples, according to your hypothesis, that application of the calculus has provided faulty results when used to analyze physical phenomena.